Databases Flashcards
Can you remote into RDS servers?
They run in Virtual machines and user cant log into those machine
Which RDS is serverless
Aurora is serverless, everything else needs a server
How Disaster recovery is done in RDS
Disaster recovery is achieved through multi AZ replication, that is data is replicated across multiple availability zones and if the data in one AZ is lost , then AWS automatically uses the one store in other AZ
What is the use of Read replicas?
They are used to improve the performance of RDS
What are the two kinds of backups for RDS?
Automated backups and Database Snapshots.
Automated backups and done in a scheduled maintenance window automatically and Database Snapshots are done manually.
How is data Secured in AWS-RDS?
Through Encryption at Rest. Key Management service is used to encrypt the data at the server
What are the different read modes in Dynamo db
Eventual consistency Reads: If data is read 1 sec after a read, then it is guaranteed to be the latest.
Strongly consistent reads: Data read is always the latest.
What is dynamo db?
schemaless, document database stored in SSD, replicated across three regions providing very high performance.
What is Redshift?
Data warehousing in the cloud. Falls under OLAP(Online Analytics processing).
It’s available in only one AZ.
Backups are enabled by default with a one day retention period to a max of 35 days
It manages 3 copies of data, the original, replica and another one in S3, Redshift can asynchronously replicate the data in S3 to another S3 for disaster recovery
What is aurora database?
It s Amazons own proprietary database, which maintains 2 copies of data in each availability zone with minimum 3 AZ. Which means we always have 6 copies of data.
Data from My sql can also be migrated to Aurora.
Use case for Elastic cache
Used to increase database and website performance by caching data in memory.Works for simple types . its simple in that its not available in multi AZ, scales horizontally. Whereas Redis can be put on multi-AZ and backed up
How many Requests can be handled by Dynamodb?
10 trillion request per day and 20 million request per second.
When to use dynamo db?
can handle millions of concurrent requests at single milliosecond delay.
No servers to maintain and it can scale automatically.
Any application which needs to be built in internet scale and has concurrency issues will benefit from Dynamodb.
How is dynamodb charged?
Pay on demand:Pay for reads and writes as it happens, good for apps with unpredictable workloads.The database scales up and down as per demand.
Pay as provisioned: Good for applications where we know how expected load.Billings happens by the hour, whether any read or write happens during that period The number of reads and writes are specified in the begining , auto scaling groups are used to grow the tables if required.
Dynamodb also charges for the stored data and any internet associated chrfes.
How is data secured in dynamodb?
Dynamo db synchronously replicates data across three availability zones in aws
Throughput limit for a single table in DynamoDb?
On Demand:
40,000 read request units and 40,000 write request units.
Provisioned:
40,000 read capacity units and 40,000 write capacity units
What is write capacity unit for a table in Dynamo Db?
One write capacity unit represents one write per second for object upto 1 kb in size
What is the minimum throughput which can be set for a table in Dynamodb?
1 RCU and 1 LCU.
What is the free tier eligibility in DynamoDb?
25 RCU and 25 WCU.
This is calculated at account level and not table level.
So it is a combination of all tables inside an account
What is the maximum amount of scan results which can be returned from dynamodb at a time.
1MB
What is the max number of RDS instances, the customer can have>
Up to 40 RDS instances. Only 10 of these can be Oracle or MS Sql, unless you have your own licenses
How to scale MySql in AWS?
You can scale storage and change the storage type for all DB engines except MS SQL
Should the RDS instance be stopped while scaling?
Scaling storage can happen while the RDS instance is running without outage however there may be performance degradation
Which Databases dont support Read replicas?
Sql Server and Oracle
What happens if a source DB instance is deleted without deleting the replicas
Each replica becomes a standalone single-AZ DB instance
What is the drawback of replicating database regionally?
The data wont be strongly consistent.
What is the difference DataMigration Service and Schema Conversion Tool
The AWS Database Migration Service can migrate your data to and from most widely used commercial and open-source databases.
Schema Conversion Tool can copy database schemas for homogenous migrations (same database) and convert schemas for heterogeneous migrations (different database)
What is one RCU in dynamoDb?
One read capacity unit represents one strongly consistent read per second, or two eventually consistent reads per second for items up to 4KB.
For items larger than 4KB, DynamoDB consumes additional read capacity units
What are the two in memory data stores in AWS?
Redis cache and Memcached.
Redis is used for simple data types and data is stored in Nodes.
Memcached can store complex types and it is persistent.Data is stored in Shards than Nodes.
What is Elasticache?
ElastiCache is a web service that makes it easy to deploy and run Memcached or Redis protocol.
The in-memory caching provided by ElastiCache can be used to significantly improve latency and throughput for many read-heavy application workloads or compute-intensive workloads
What is Redshift spectrum?
Tool in redshift to query directly from data files on S3.
How other AWS services can access S3 without traversing the public network.
By using a S3 VPC endpoint
